Add distance and inflection count metric

Add the two simple metric to the tortuosity module. Basically, the widget
calls the logic on the spatial object node depending on the selected
checkboxes.
Also add the Inflection points metric that show the inflection value at
each point of the vessel.
Add sum of angle metric to the tortuosity logic

Add the missing sum of angles metric to the tortuosity logic.
Take advantage of this to factorize some of the copy methods in a namespace
for clarity.
Add testing - WIP